On Sentences Which are True of Direct Unions of Algebras. - Alfred Horn (J. Symb. Log., 1951)

The Separation Theorem of Intuitionist Propositional Calculus. - Alfred Horn (J. Symb. Log., 1962)

Logic with Truth Values in a Linearly Ordered Heyting Algebra. - Alfred Horn (J. Symb. Log., 1969)

Free L-Algebras. - Alfred Horn (J. Symb. Log., 1969)

Logics Which Are Characterized by Subresiduated Lattices. - George Epstein; Alfred Horn (Math. Log. Q., 1976)

Free S5 algebras. - Alfred Horn (Notre Dame J. Formal Log., 1978)